JPH03252033A - Gas phase ion source - Google Patents

Abstract

PURPOSE:To made helium gas in the vicinity of an emitter less than 10<-4>Torr in pressure even when accelerating voltage is made high by employing a throttle in a pressure changing means wherein the throttle is made up in such a way that a bar shaped member is inserted into the hole of an aperture plate while a little gap is provided between the hole and the member. CONSTITUTION:A throttle is disposed, which is so constituted that the conical section of a cone 20 is coupled in the hole 19S of an aperture plate 19 while the other end of the cone is bonded on the aperture plate 19. When helium gas of somewhat 1ATM. is applied to a pipe 11', the conical section at the tip end of the cone 20 is pressed intensely against the hole 19S so that a contact section between the conical section at the tip end of the cone 20 and the hole 19S is kept less than 10<-8>l/s in conductance. Namely, this is substantially equiva lent to a state that the throttle the hole diameter of which is less than 0.5mum, is provided. By this constitution, even when highly accelerating voltage of some what 100KV is applied to an emitter 8, the pressure less than 10<-4>Torr of helium gas in the vicinity of the emitter can be secured with no discharge induced along the inner surface of the pipe 11' and in helium gas.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gas phase ion source capable of applying a high acceleration voltage.

(Prior Art) Recently, an ion beam device using a gas phase ion source has been developed.

This gas phase ion source is an ion source that supplies a gas as an ion species, such as helium gas or hydrogen, to an emitter tip formed with a sharp tip, and ionizes the dregs molecules by a strong electric field.

In such an ion source, in order to apply a high voltage to the emitter and increase the beam current, the emitter is
It needs to be cooled to extremely low temperatures, around 30°F. For this reason, a structure as shown in FIG. 3 has been developed.

In Fig. 3, 1 is the outer wall of the ion source whose interior is kept in a high vacuum, and 2 is a tank filled with a coolant such as liquid helium 3, which is inserted into the insulating part of the opening 4 formed at the top of the outer wall 1 of the ion source. It is supported in a thermally insulated state via a stainless steel bellows 5. Reference numeral 6 is an electrically insulating material with high thermal conductivity, such as sapphire, fixed to the bottom of the tank 2, and an emitter 8 having a sharp tip is held in the center of the bottom of the sapphire via a holder 7.

9 is a bow-circular electrode placed opposite to this emitter 8;
An ion passage hole 9a is formed in the center, and
This extraction electrode is supported by the sapphire 6 via a support tube 10 made of an electrically insulating material. Reference numeral 11 denotes a vibrator for introducing a gas as an ion species, such as helium gas, into the vicinity of the emitter 8. One end of this vibrator is attached to the side wall of the support tube 10 by penetrating it, and the other end is attached to a heat exchanger. It is connected to a gas cylinder (not shown) filled with helium gas via a container 12.

Liquid nitrogen 13 is introduced into the heat exchanger 12 . 14 is a supply pipe for supplying liquid helium into the tank 2, and 15 is a discharge pipe for discharging the helium gas vaporized within the tank 2. Reference numeral 16 denotes a lid for closing the opening 4, and is made of a heat insulating material.

By doing so, the emitter 8 is electrically insulated by the sapphire 6 from the ion source outer wall 1 and the tank 2 which are at ground potential, and at the same time is cooled through the sapphire. Therefore, 50K is applied to this emitter from an accelerating electric field not shown.
Applying an accelerating voltage of about V, the emitter 8 and extraction electrode 9
If helium gas is supplied from the vibrator 11 to the vicinity of the emitter while applying an extraction voltage of several tens of kilovolts between the Ionized by the strong electric field between the electrodes. Ions generated by this ionization are extracted by an extraction voltage and simultaneously accelerated toward an anode (not shown) by an accelerating voltage.

In such a configuration, when normal temperature helium gas is introduced from the vibrator 11, the emitter 8 reaches the liquid helium temperature (4
Since it is no longer possible to cool the helium gas to a temperature of about 100.degree. As a result, a heat exchanger must be provided, which complicates the configuration and increases costs.

FIG. 4 is a schematic diagram of a gas phase ion source proposed to solve such problems. In the figure, the same components as in FIG. 2 are denoted by the same numbers.

In the gas phase ion source shown in FIG. 4, a vibrator 11- for supplying gas to be ionized is connected to a refrigerant 3
It is designed to be inserted inside.

In the figure, 17a and 17b indicate the inside of the support tube 10 and the vibrator 11.
A gas passage is formed in the bottom of the tank 2 and in the sapphire 6 to connect the emitter 8, and a gas passage 18 is a constrictor that reduces the pressure of the helium gas introduced near the emitter 8 to 10-' Torr or less to prevent arc discharge. It is for.

With this configuration, the vibrator 11' is cooled by the refrigerant 3 for cooling the emitter 8, so room temperature helium gas can be directly introduced into the ion source outer wall 1 without providing an independent heat exchanger. Also, as this gas passes through the tank 2, it is cooled to liquid helium temperature. After the pressure is reduced to a predetermined pressure by the throttle 18, the gas passage 1
Since it is guided into the support tube 10 through 7a117b, that is, near the emitter 8, the temperature of the emitter 8 does not rise and can be maintained at the liquid helium temperature.

(Problem to be Solved by the Invention) When a high accelerating voltage is applied to the emitter 8 from an accelerating power source (not shown), a high accelerating voltage is applied to the creeping surface of the vibrator 11- and into the vibrator 11'. Electric discharge occurs in helium gas. As a method for preventing the discharge, the vibrator 1
It is conceivable to increase the length of 1', but this would increase the size of the entire ion source. Therefore, as shown in FIG. 4, the discharge is prevented by providing a throttle to increase the gas pressure of the helium gas supplied to the vibrator 11'.

However, when an accelerating voltage of, for example, about 100 KV is applied to the emitter 8, even if helium gas of about 1 atm is supplied to the vibrator 11'', the pressure of the helium gas near the emitter 8 is reduced to 10-'Torr or less. In order to do this, 1O-
81)/s or less is required. Such a diaphragm corresponds to a diaphragm with a hole diameter of 0.5 μm or less, but it is extremely difficult to manufacture a diaphragm with such a small pore diameter.

An object of the present invention is to provide a novel gas phase ion source equipped with an aperture that allows the pressure of helium gas near the emitter to be set to 10-'Toor or less even when the accelerating voltage is increased.

(Means for Solving the Problems) For this purpose, the present invention provides an emitter to which a high voltage is applied, a tank for storing a refrigerant for cooling the emitter, and a drawer disposed opposite to the emitter and having a drawer between the emitter and the emitter. An extraction electrode to which a voltage is applied, a pipe inserted into the refrigerant and supplying gas to be ionized near the emitter, and a small gap provided in the pipe and between the hole in the aperture plate and the reading plate. We have invented a gas phase ion source consisting of a constrictor body into which rod-shaped members are fitted, and a vacuum container housing these members.

(Embodiment) FIG. 1 shows an embodiment of a diaphragm which is a main part of the present invention.

In the figure, 19 is a hole 19S with a hole diameter of about 0.1 mm, for example.
The aperture plate 20 is, for example, a cone having an outer diameter of about 0.125 mm and a conical tip formed by electric field etching. The conical portion of the cone is fitted into the hole 19S of the aperture plate 19, and the other end of the cone is bonded to the aperture plate 19.

A diaphragm having such a configuration is the diaphragm 18 shown in FIG.
Place it instead of . At this time, as shown in FIG. 1, the aperture is fixed to the inner wall so that no gas leaks between the inner wall of the pipe 11' into which the gas to be ionized is introduced and the outer periphery of the aperture. Then, when helium gas of about 1 atmosphere is supplied to the pipe 11', the conical portion at the tip of the cone 20 is strongly pressed against the hole 19S of the aperture plate 19.
The tip # of the cone 20 and the hole 1 of the aperture plate 19
The conductance of the contact portion of the 9S portion is maintained at 10−811/s or less. That is, the pore diameter is 0. This is substantially the same state as if a diaphragm of 5 μm or less was provided.

Therefore, even when a high accelerating voltage of, for example, about 100 KV is applied to the emitter 8, no discharge occurs along the surface of the pipe 11' or in the helium gas of the bi 111'.
The helium gas pressure near the emitter is set to 10-'To
It can be made below rr.

Now, the conductance in the aperture can be varied by changing the hole diameter of the aperture plate 19, the opening angle of the conical portion at the tip of the cone 20, the surface roughness of the hole of the aperture plate 19, etc.

In addition, as a modification of the aperture, as shown in FIG. 2(a),
A cone 20 with a constant diameter portion inserted into the hole of the aperture plate 19, or several aperture plates 19A and 19B as shown in FIG. 2(b).

19C may be superimposed, and a cone 20 may be inserted into the hole of each of the superimposed apertures to finely adjust the conductance.

(Effects) The present invention provides an emitter to which a high voltage is applied, a tank containing a refrigerant for cooling the emitter, an extraction electrode placed opposite to the emitter and to which an extraction voltage is applied between the emitter and the emitter. A gas phase ion source consisting of a pipe inserted into a refrigerant and supplying a gas to be ionized near the emitter, a throttle as a pressure variable means provided in the pipe, and a vacuum container housing these members, As the diaphragm used as a pressure variable means, we used an easily manufactured diaphragm consisting of a rod-shaped member fitted into the hole of the aperture plate to create a small gap between it and the reading plate, so even if the accelerating voltage was high, , the pressure of helium gas near the emitter can be realized to be 10 −4 or less.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an aperture diaphragm showing one embodiment of the present invention;
The figures are configuration diagrams of an aperture according to a modification of the present invention, Figures 3 and 4.
The figure is a block diagram of a conventional gas phase ion source.

Claims (1)

[Claims] An emitter to which a high voltage is applied, a tank containing a refrigerant for cooling the emitter, an extraction electrode placed opposite to the emitter and to which an extraction voltage is applied between the emitter and the emitter;
A pipe that is inserted into the refrigerant and supplies the gas to be ionized near the emitter, and a rod-shaped member that is installed in the pipe and has a small gap between the hole and the hole of the aperture plate is fitted. A gas phase ion source consisting of a constrictor and a vacuum container that houses these members.